1. Field of the Invention
The present invention relates to a method and apparatus for perforating corrugated tubing. More particularly, the present invention relates to a method and apparatus for perforating corrugated tubing as the tubing is being moved at a high speed therethrough. Even more particularly, the present invention related to a method and apparatus for perforating corrugated tubing which is selectively interruptable to leave portions of the tubing uncut.
2. Description of the Background Art
Machines for perforating corrugated tubing have been in use for some time. One such machine is disclosed in U.S. Pat. No. 3,824,886, to Hegler, which teaches an apparatus for cutting apertures in corrugated tubing by rotating a cutter circumferentially around the tubing. The cutter of Hegler is disposed in a ridge on a wheel, which is driven by a transmission. The wheel and cutter cooperate with a roller to rotate spirally around the tubing. While offering a relatively simple design to achieve its ends, the apparatus of Hegler is necessarily limited to a relatively low speed operation due to the necessity of the wheel and cutter traveling the entire length of the corrugation. Increasing the traveling speed of the wheel beyond modest levels would result in miscuts in the tubing, such as cuts in the side walls of the corrugations instead of the valleys thereof. Further, excessive wheel speed could cause the wheel to jump past some corrugations, thus missing areas of the tubing and leaving those areas unperforated.
U.S. Pat. No. 4,180,357 to Lupke et al. discloses another apparatus for perforating corrugated tubing, which has multiple lead screws for driving tubing along an axial path, the lead screws meshingly engaging with the corrugations of the tubing. Each of the lead screws is mounted on an axis of rotation parallel to the axial path of the tubing, and each lead screw carries a cutter thereon, flanked on each side by a raised rib. The cutter is in a plane substantially at a right angle to the axial path, and the cutter intermittently intersects the tubing. The apparatus of Lupke rotates the lead screws using a system of gear wheels which are coordinated such that pairs of lead screws cut the tubing simultaneously. The apparatus of Lupke can cut tubing at a maximum horizontal speed of 20 feet/minute. At greater speeds, the apparatus experiences difficulty in properly aligning the cutter and perforating the tubing.
An improvement on the basic design of Lupke is disclosed in U.S. Pat. No. 4,218,164, also issued to Lupke et al., in which a plurality of helically raised ribs are centrally disposed on lead screw members, replacing the straight ribs of the Lupke '357 patent. A cutter is disposed at the end of each helical rib. The helical rib tends to facilitate entry of the cutter into the valley of the corrugation. The rib of the Lupke '164 apparatus extends around only a portion of the circumference of the shaft, thus continuing the teaching of intermittent intersection of the tubing by the cutter, as taught in the earlier Lupke patent. The apparatus of the Lupke '164 patent achieves a horizontal tubing speed of about 40 to 50 feet/minute. At speeds in excess of 50 feet/minute, the second Lupke apparatus tends to climb the side walls of the corrugations and to perforate either those side walls or the crown of the corrugation. Lupke et al. overcame the limitation of rotating the entire cutter wheel around the tubing as taught in Hegler. In the first Lupke apparatus, the plurality of raised ribs essentially slowed the horizontal movement of the tubing long enough to effect the perforation. The second Lupke apparatus substituted the helical rib for the plurality of straight ribs, alleviating the need to slow or stop the horizontal travel of the tubing to effect the perforation. However, when attempting to operate the second Lupke apparatus at speeds in excess of 50 feet/minute, miscuts are experienced. Also, problems are encountered with the feed worms of Lupke. At high speeds, the vertical sides of the feed worms are unable to maintain their helical course in the corrugation. Thus, the worms tend to climb the side walls of the corrugations, crushing the crown of the tubing and skipping parts of the corrugation. Also, neither Lupke or the other available art teaches any method of intermittent cutting, that is, controlled perforation of corrugated tubing which can be intentionally selectively interrupted to leave a portion of the tubing uncut.
A need still exists in the art for a reliable high-speed apparatus for perforating corrugated tubing. Ideally, such an apparatus would be temporarily selectively interruptible to pause in perforating tubing during operation thereof, to leave selected portions of tubing unperforated.